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PERLRECHARCLASS(1)     Perl Programmers Reference Guide     PERLRECHARCLASS(1)



NAME
       perlrecharclass - Perl Regular Expression Character Classes

DESCRIPTION
       The top level documentation about Perl regular expressions is found in perlre.

       This manual page discusses the syntax and use of character classes in Perl Regular Expressions.

       A character class is a way of denoting a set of characters, in such a way that one character of the set is
       matched.  It's important to remember that matching a character class consumes exactly one character in the
       source string. (The source string is the string the regular expression is matched against.)

       There are three types of character classes in Perl regular expressions: the dot, backslashed sequences, and the
       bracketed form.

   The dot
       The dot (or period), "." is probably the most used, and certainly the most well-known character class. By
       default, a dot matches any character, except for the newline. The default can be changed to add matching the
       newline with the single line modifier: either for the entire regular expression using the "/s" modifier, or
       locally using "(?s)".

       Here are some examples:

        "a"  =~  /./       # Match
        "."  =~  /./       # Match
        ""   =~  /./       # No match (dot has to match a character)
        "\n" =~  /./       # No match (dot does not match a newline)
        "\n" =~  /./s      # Match (global 'single line' modifier)
        "\n" =~  /(?s:.)/  # Match (local 'single line' modifier)
        "ab" =~  /^.$/     # No match (dot matches one character)

   Backslashed sequences
       Perl regular expressions contain many backslashed sequences that constitute a character class. That is, they
       will match a single character, if that character belongs to a specific set of characters (defined by the
       sequence). A backslashed sequence is a sequence of characters starting with a backslash. Not all backslashed
       sequences are character class; for a full list, see perlrebackslash.

       Here's a list of the backslashed sequences, which are discussed in more detail below.

        \d             Match a digit character.
        \D             Match a non-digit character.
        \w             Match a "word" character.
        \W             Match a non-"word" character.
        \s             Match a white space character.
        \S             Match a non-white space character.
        \h             Match a horizontal white space character.
        \H             Match a character that isn't horizontal white space.
        \v             Match a vertical white space character.
        \V             Match a character that isn't vertical white space.
        \pP, \p{Prop}  Match a character matching a Unicode property.
        \PP, \P{Prop}  Match a character that doesn't match a Unicode property.

       Digits

       "\d" matches a single character that is considered to be a digit.  What is considered a digit depends on the
       internal encoding of the source string. If the source string is in UTF-8 format, "\d" not only matches the
       digits '0' - '9', but also Arabic, Devanagari and digits from other languages. Otherwise, if there is a locale
       in effect, it will match whatever characters the locale considers digits. Without a locale, "\d" matches the
       digits '0' to '9'.  See "Locale, Unicode and UTF-8".

       Any character that isn't matched by "\d" will be matched by "\D".

       Word characters

       "\w" matches a single word character: an alphanumeric character (that is, an alphabetic character, or a digit),
       or the underscore ("_").  What is considered a word character depends on the internal encoding of the string.
       If it's in UTF-8 format, "\w" matches those characters that are considered word characters in the Unicode
       database. That is, it not only matches ASCII letters, but also Thai letters, Greek letters, etc.  If the source
       string isn't in UTF-8 format, "\w" matches those characters that are considered word characters by the current
       locale. Without a locale in effect, "\w" matches the ASCII letters, digits and the underscore.

       Any character that isn't matched by "\w" will be matched by "\W".

       White space

       "\s" matches any single character that is consider white space. In the ASCII range, "\s" matches the horizontal
       tab ("\t"), the new line ("\n"), the form feed ("\f"), the carriage return ("\r"), and the space (the vertical
       tab, "\cK" is not matched by "\s").  The exact set of characters matched by "\s" depends on whether the source
       string is in UTF-8 format. If it is, "\s" matches what is considered white space in the Unicode database.
       Otherwise, if there is a locale in effect, "\s" matches whatever is considered white space by the current
       locale. Without a locale, "\s" matches the five characters mentioned in the beginning of this paragraph.
       Perhaps the most notable difference is that "\s" matches a non-breaking space only if the non-breaking space is
       in a UTF-8 encoded string.

       Any character that isn't matched by "\s" will be matched by "\S".

       "\h" will match any character that is considered horizontal white space; this includes the space and the tab
       characters. "\H" will match any character that is not considered horizontal white space.

       "\v" will match any character that is considered vertical white space; this includes the carriage return and
       line feed characters (newline).  "\V" will match any character that is not considered vertical white space.

       "\R" matches anything that can be considered a newline under Unicode rules. It's not a character class, as it
       can match a multi-character sequence. Therefore, it cannot be used inside a bracketed character class. Details
       are discussed in perlrebackslash.

       "\h", "\H", "\v", "\V", and "\R" are new in perl 5.10.0.

       Note that unlike "\s", "\d" and "\w", "\h" and "\v" always match the same characters, regardless whether the
       source string is in UTF-8 format or not. The set of characters they match is also not influenced by locale.

       One might think that "\s" is equivalent with "[\h\v]". This is not true.  The vertical tab ("\x0b") is not
       matched by "\s", it is however considered vertical white space. Furthermore, if the source string is not in
       UTF-8 format, the next line ("\x85") and the no-break space ("\xA0") are not matched by "\s", but are by "\v"
       and "\h" respectively.  If the source string is in UTF-8 format, both the next line and the no-break space are
       matched by "\s".

       The following table is a complete listing of characters matched by "\s", "\h" and "\v".

       The first column gives the code point of the character (in hex format), the second column gives the (Unicode)
       name. The third column indicates by which class(es) the character is matched.

        0x00009        CHARACTER TABULATION   h s
        0x0000a              LINE FEED (LF)    vs
        0x0000b             LINE TABULATION    v
        0x0000c              FORM FEED (FF)    vs
        0x0000d        CARRIAGE RETURN (CR)    vs
        0x00020                       SPACE   h s
        0x00085             NEXT LINE (NEL)    vs  [1]
        0x000a0              NO-BREAK SPACE   h s  [1]
        0x01680            OGHAM SPACE MARK   h s
        0x0180e   MONGOLIAN VOWEL SEPARATOR   h s
        0x02000                     EN QUAD   h s
        0x02001                     EM QUAD   h s
        0x02002                    EN SPACE   h s
        0x02003                    EM SPACE   h s
        0x02004          THREE-PER-EM SPACE   h s
        0x02005           FOUR-PER-EM SPACE   h s
        0x02006            SIX-PER-EM SPACE   h s
        0x02007                FIGURE SPACE   h s
        0x02008           PUNCTUATION SPACE   h s
        0x02009                  THIN SPACE   h s
        0x0200a                  HAIR SPACE   h s
        0x02028              LINE SEPARATOR    vs
        0x02029         PARAGRAPH SEPARATOR    vs
        0x0202f       NARROW NO-BREAK SPACE   h s
        0x0205f   MEDIUM MATHEMATICAL SPACE   h s
        0x03000           IDEOGRAPHIC SPACE   h s

       [1] NEXT LINE and NO-BREAK SPACE only match "\s" if the source string is in UTF-8 format.

       It is worth noting that "\d", "\w", etc, match single characters, not complete numbers or words. To match a
       number (that consists of integers), use "\d+"; to match a word, use "\w+".

       Unicode Properties

       "\pP" and "\p{Prop}" are character classes to match characters that fit given Unicode classes. One letter
       classes can be used in the "\pP" form, with the class name following the "\p", otherwise, the property name is
       enclosed in braces, and follows the "\p". For instance, a match for a number can be written as "/\pN/" or as
       "/\p{Number}/".  Lowercase letters are matched by the property LowercaseLetter which has as short form Ll. They
       have to be written as "/\p{Ll}/" or "/\p{LowercaseLetter}/". "/\pLl/" is valid, but means something different.
       It matches a two character string: a letter (Unicode property "\pL"), followed by a lowercase "l".

       For a list of possible properties, see "Unicode Character Properties" in perlunicode. It is also possible to
       defined your own properties. This is discussed in "User-Defined Character Properties" in perlunicode.

       Examples

        "a"  =~  /\w/      # Match, "a" is a 'word' character.
        "7"  =~  /\w/      # Match, "7" is a 'word' character as well.
        "a"  =~  /\d/      # No match, "a" isn't a digit.
        "7"  =~  /\d/      # Match, "7" is a digit.
        " "  =~  /\s/      # Match, a space is white space.
        "a"  =~  /\D/      # Match, "a" is a non-digit.
        "7"  =~  /\D/      # No match, "7" is not a non-digit.
        " "  =~  /\S/      # No match, a space is not non-white space.

        " "  =~  /\h/      # Match, space is horizontal white space.
        " "  =~  /\v/      # No match, space is not vertical white space.
        "\r" =~  /\v/      # Match, a return is vertical white space.

        "a"  =~  /\pL/     # Match, "a" is a letter.
        "a"  =~  /\p{Lu}/  # No match, /\p{Lu}/ matches upper case letters.

        "\x{0e0b}" =~ /\p{Thai}/  # Match, \x{0e0b} is the character
                                  # 'THAI CHARACTER SO SO', and that's in
                                  # Thai Unicode class.
        "a"  =~  /\P{Lao}/ # Match, as "a" is not a Laoian character.

   Bracketed Character Classes
       The third form of character class you can use in Perl regular expressions is the bracketed form. In its
       simplest form, it lists the characters that may be matched inside square brackets, like this: "[aeiou]".  This
       matches one of "a", "e", "i", "o" or "u". Just as the other character classes, exactly one character will be
       matched. To match a longer string consisting of characters mentioned in the characters class, follow the
       character class with a quantifier. For instance, "[aeiou]+" matches a string of one or more lowercase ASCII
       vowels.

       Repeating a character in a character class has no effect; it's considered to be in the set only once.

       Examples:

        "e"  =~  /[aeiou]/        # Match, as "e" is listed in the class.
        "p"  =~  /[aeiou]/        # No match, "p" is not listed in the class.
        "ae" =~  /^[aeiou]$/      # No match, a character class only matches
                                  # a single character.
        "ae" =~  /^[aeiou]+$/     # Match, due to the quantifier.

       Special Characters Inside a Bracketed Character Class

       Most characters that are meta characters in regular expressions (that is, characters that carry a special
       meaning like "*" or "(") lose their special meaning and can be used inside a character class without the need
       to escape them. For instance, "[()]" matches either an opening parenthesis, or a closing parenthesis, and the
       parens inside the character class don't group or capture.

       Characters that may carry a special meaning inside a character class are: "\", "^", "-", "[" and "]", and are
       discussed below. They can be escaped with a backslash, although this is sometimes not needed, in which case the
       backslash may be omitted.

       The sequence "\b" is special inside a bracketed character class. While outside the character class "\b" is an
       assertion indicating a point that does not have either two word characters or two non-word characters on either
       side, inside a bracketed character class, "\b" matches a backspace character.

       A "[" is not special inside a character class, unless it's the start of a POSIX character class (see below). It
       normally does not need escaping.

       A "]" is either the end of a POSIX character class (see below), or it signals the end of the bracketed
       character class. Normally it needs escaping if you want to include a "]" in the set of characters.  However, if
       the "]" is the first (or the second if the first character is a caret) character of a bracketed character
       class, it does not denote the end of the class (as you cannot have an empty class) and is considered part of
       the set of characters that can be matched without escaping.

       Examples:

        "+"   =~ /[+?*]/     #  Match, "+" in a character class is not special.
        "\cH" =~ /[\b]/      #  Match, \b inside in a character class
                             #  is equivalent with a backspace.
        "]"   =~ /[][]/      #  Match, as the character class contains.
                             #  both [ and ].
        "[]"  =~ /[[]]/      #  Match, the pattern contains a character class
                             #  containing just ], and the character class is
                             #  followed by a ].

       Character Ranges

       It is not uncommon to want to match a range of characters. Luckily, instead of listing all the characters in
       the range, one may use the hyphen ("-").  If inside a bracketed character class you have two characters
       separated by a hyphen, it's treated as if all the characters between the two are in the class. For instance,
       "[0-9]" matches any ASCII digit, and "[a-m]" matches any lowercase letter from the first half of the ASCII
       alphabet.

       Note that the two characters on either side of the hyphen are not necessary both letters or both digits. Any
       character is possible, although not advisable.  "['-?]" contains a range of characters, but most people will
       not know which characters that will be. Furthermore, such ranges may lead to portability problems if the code
       has to run on a platform that uses a different character set, such as EBCDIC.

       If a hyphen in a character class cannot be part of a range, for instance because it is the first or the last
       character of the character class, or if it immediately follows a range, the hyphen isn't special, and will be
       considered a character that may be matched. You have to escape the hyphen with a backslash if you want to have
       a hyphen in your set of characters to be matched, and its position in the class is such that it can be
       considered part of a range.

       Examples:

        [a-z]       #  Matches a character that is a lower case ASCII letter.
        [a-fz]      #  Matches any letter between 'a' and 'f' (inclusive) or the
                    #  letter 'z'.
        [-z]        #  Matches either a hyphen ('-') or the letter 'z'.
        [a-f-m]     #  Matches any letter between 'a' and 'f' (inclusive), the
                    #  hyphen ('-'), or the letter 'm'.
        ['-?]       #  Matches any of the characters  '()*+,-./0123456789:;<=>?
                    #  (But not on an EBCDIC platform).

       Negation

       It is also possible to instead list the characters you do not want to match. You can do so by using a caret
       ("^") as the first character in the character class. For instance, "[^a-z]" matches a character that is not a
       lowercase ASCII letter.

       This syntax make the caret a special character inside a bracketed character class, but only if it is the first
       character of the class. So if you want to have the caret as one of the characters you want to match, you either
       have to escape the caret, or not list it first.

       Examples:

        "e"  =~  /[^aeiou]/   #  No match, the 'e' is listed.
        "x"  =~  /[^aeiou]/   #  Match, as 'x' isn't a lowercase vowel.
        "^"  =~  /[^^]/       #  No match, matches anything that isn't a caret.
        "^"  =~  /[x^]/       #  Match, caret is not special here.

       Backslash Sequences

       You can put a backslash sequence character class inside a bracketed character class, and it will act just as if
       you put all the characters matched by the backslash sequence inside the character class. For instance,
       "[a-f\d]" will match any digit, or any of the lowercase letters between 'a' and 'f' inclusive.

       Examples:

        /[\p{Thai}\d]/     # Matches a character that is either a Thai
                           # character, or a digit.
        /[^\p{Arabic}()]/  # Matches a character that is neither an Arabic
                           # character, nor a parenthesis.

       Backslash sequence character classes cannot form one of the endpoints of a range.

       Posix Character Classes

       Posix character classes have the form "[:class:]", where class is name, and the "[:" and ":]" delimiters. Posix
       character classes appear inside bracketed character classes, and are a convenient and descriptive way of
       listing a group of characters. Be careful about the syntax,

        # Correct:
        $string =~ /[[:alpha:]]/

        # Incorrect (will warn):
        $string =~ /[:alpha:]/

       The latter pattern would be a character class consisting of a colon, and the letters "a", "l", "p" and "h".

       Perl recognizes the following POSIX character classes:

        alpha  Any alphabetical character.
        alnum  Any alphanumerical character.
        ascii  Any ASCII character.
        blank  A GNU extension, equal to a space or a horizontal tab ("\t").
        cntrl  Any control character.
        digit  Any digit, equivalent to "\d".
        graph  Any printable character, excluding a space.
        lower  Any lowercase character.
        print  Any printable character, including a space.
        punct  Any punctuation character.
        space  Any white space character. "\s" plus the vertical tab ("\cK").
        upper  Any uppercase character.
        word   Any "word" character, equivalent to "\w".
        xdigit Any hexadecimal digit, '0' - '9', 'a' - 'f', 'A' - 'F'.

       The exact set of characters matched depends on whether the source string is internally in UTF-8 format or not.
       See "Locale, Unicode and UTF-8".

       Most POSIX character classes have "\p" counterparts. The difference is that the "\p" classes will always match
       according to the Unicode properties, regardless whether the string is in UTF-8 format or not.

       The following table shows the relation between POSIX character classes and the Unicode properties:

        [[:...:]]   \p{...}      backslash

        alpha       IsAlpha
        alnum       IsAlnum
        ascii       IsASCII
        blank
        cntrl       IsCntrl
        digit       IsDigit      \d
        graph       IsGraph
        lower       IsLower
        print       IsPrint
        punct       IsPunct
        space       IsSpace
                    IsSpacePerl  \s
        upper       IsUpper
        word        IsWord
        xdigit      IsXDigit

       Some character classes may have a non-obvious name:

       cntrl
           Any control character. Usually, control characters don't produce output as such, but instead control the
           terminal somehow: for example newline and backspace are control characters. All characters with "ord()"
           less than 32 are usually classified as control characters (in ASCII, the ISO Latin character sets, and
           Unicode), as is the character "ord()" value of 127 ("DEL").

       graph
           Any character that is graphical, that is, visible. This class consists of all the alphanumerical characters
           and all punctuation characters.

       print
           All printable characters, which is the set of all the graphical characters plus the space.

       punct
           Any punctuation (special) character.

       Negation

       A Perl extension to the POSIX character class is the ability to negate it. This is done by prefixing the class
       name with a caret ("^").  Some examples:

        POSIX         Unicode       Backslash
        [[:^digit:]]  \P{IsDigit}   \D
        [[:^space:]]  \P{IsSpace}   \S
        [[:^word:]]   \P{IsWord}    \W

       [= =] and [. .]

       Perl will recognize the POSIX character classes "[=class=]", and "[.class.]", but does not (yet?) support this
       construct. Use of such a construct will lead to an error.

       Examples

        /[[:digit:]]/            # Matches a character that is a digit.
        /[01[:lower:]]/          # Matches a character that is either a
                                 # lowercase letter, or '0' or '1'.
        /[[:digit:][:^xdigit:]]/ # Matches a character that can be anything,
                                 # but the letters 'a' to 'f' in either case.
                                 # This is because the character class contains
                                 # all digits, and anything that isn't a
                                 # hex digit, resulting in a class containing
                                 # all characters, but the letters 'a' to 'f'
                                 # and 'A' to 'F'.

   Locale, Unicode and UTF-8
       Some of the character classes have a somewhat different behaviour depending on the internal encoding of the
       source string, and the locale that is in effect.

       "\w", "\d", "\s" and the POSIX character classes (and their negations, including "\W", "\D", "\S") suffer from
       this behaviour.

       The rule is that if the source string is in UTF-8 format, the character classes match according to the Unicode
       properties. If the source string isn't, then the character classes match according to whatever locale is in
       effect. If there is no locale, they match the ASCII defaults (52 letters, 10 digits and underscore for "\w", 0
       to 9 for "\d", etc).

       This usually means that if you are matching against characters whose "ord()" values are between 128 and 255
       inclusive, your character class may match or not depending on the current locale, and whether the source string
       is in UTF-8 format. The string will be in UTF-8 format if it contains characters whose "ord()" value exceeds
       255. But a string may be in UTF-8 format without it having such characters.

       For portability reasons, it may be better to not use "\w", "\d", "\s" or the POSIX character classes, and use
       the Unicode properties instead.

       Examples

        $str =  "\xDF";      # $str is not in UTF-8 format.
        $str =~ /^\w/;       # No match, as $str isn't in UTF-8 format.
        $str .= "\x{0e0b}";  # Now $str is in UTF-8 format.
        $str =~ /^\w/;       # Match! $str is now in UTF-8 format.
        chop $str;
        $str =~ /^\w/;       # Still a match! $str remains in UTF-8 format.



perl v5.10.1                      2009-05-14                PERLRECHARCLASS(1)